B757 Captain discovered his cleared PDC route including the identifier 'Q1' could be programmed and accepted by the FMC in two distinctly different ways; only one of which was correct.

Narrative

PDC cleared route was SEA ELMAA Q1 PYE SFO. This is an ambiguous clearance which I resolved prior to departure; but am writing this as it is a serious possibility that it could cause an accident in the future. Q1 is BOTH a route (a 'quick route' RNAV airway) AND a fix... i.e. it can be programmed to either the left side OR the right side of the FMC and will appear as a valid routing and you would have no way of knowing which is correct. If selected as a route; the route reads ELMAA; then along the Q1 routing to PYE. If selected as a fix; the route reads ELMAA; then direct to Q1; then direct to PYE. The way the routing reads on the PDC; either could be correct. Fortunately for me; the point Q1 is way out of the way (N5842.6m W09830.3 in Northeastern Canada) so it was obvious; but if we had started out somewhere else; it would have been less obvious. So; ATC needs to either rename the point OR rename the route; so both are not the same; else; the potential exists for a future flight to go the wrong way and possibly end up in real trouble.